Nowadays, orthogonal frequency duplex modulation (OFDM) technique has become the most popular modulation method, which uses power amplifier (PA) to achieve the linearization. The power amplifier in the wireless transceivers often meet the phenomenon of amplitude-modulation to phase-modulation (AM-PM) distortion, and the problems of the spectral regrowth are accordingly occurred. This spectral regrowth not only results in the difficulty to the construction of the PA in the wireless transceiver, but also reduces the performances such as transmitter mask and error vector magnitude (EVM) in the transceiver upon applying in IEEE 802.11a/b/g/n wireless local area network (WLAN) application.
A current linearization technique of power amplifier is the Cartesian feedback, where the output of the power amplifier is decomposed into quadrature phases by the feedback before it is compared with the inputs. The drawbacks lie in that the demodulator and the differential amplifier in the feedback path could increase the system complexity and the unit cost.
Another current linearization technique of power amplifier is the adaptive digital predistortion, which converts the output of the power amplifier in the downstream path to the baseband so as to obtain the amplitude and the phase error signals and the adaptively predistort input signal, thereby correct the distortions of AM-AM and AM-PM of the power amplifier. The drawbacks lie in that the bandwidth of the baseband signal would be increased and more power dissipation would be made. In addition, since different statuses exist between the calibration operation and the normal operation, the performance of the system predistortion would be reduced by the electrical mutual coupling between the up-conversion path and the down-conversion path.
It is therefore attempted by the applicant to deal with the above situation encountered in the prior art.